The invention relates to the protection of radio engineering installations, especially antennae, against the influences of the weather, in the form of a tower or cupola-shaped casing supported by a carrying mechanism and made of hard plastic, especially a plastic having a polyurethane base.
Such a casing is known from German Pat. No. 12 73 023. In this known casing, segments are pre-manufactured from polyurethane hard foam in easily transportable sizes and are connected at the erection site by adhesion. For example, individual casing-shaped sections, each consisting of, for example, 12 segments, are made which, placed on top of one another, may form a tower-like casing for, for example, antennae. In case of a covering of long antenna masts, a lateral positional security of the casing, which is self-supporting in the manner described, is accomplished by carrying mechanisms disposed on the antenna mast, especially in the area of the platforms disposed one above the other of customary radio antenna masts. Similarly, an essentially ball or ball-calotte-shaped covering or casing for rotatably movable antennae may be developed, say for radar monitoring, which may be placed on a construction at the building site.
Since antennae, especially radio antennae, are erected on exposed locations, such as hills, mountains, buildings, such as TV towers, etc., as is well known, in order to obtain as far a reach as possible, said antenna masts and their covering are regularly exposed to considerable lateral thrusts due to wind. These lateral thrusts due to wind, when flowing around the casing, create corresponding pressure and suction loads which try to deform the casing. Furthermore, the lateral thrusts due to wind lead often to considerable vibrational deflections, especially of long antenna masts, and because of vibration stimulation as a result of shedding of vortices at the periphery of the casing and of the building carrying the masts, lead to natural vibrations, especially of the antenna masts, the vibrational deflections of which, in turn, are introduced into the casing. As a result of that, the wall of a casing consisting of hard plastic is subject to considerable rapidly changing tension and buckling loads, which lead to a considerable and disturbing development of noise. Finally, the changing of the permanent loads of the casing will lead to fatigue of the material and thus to breakdowns.
Besides loads on the casing or covering caused by wind, which occur also in shorter but larger cupolas, say, for example, radar antennae, there also occur loads due to heat expansion. Especially in conjunction with such additional loads, the load caused by wind may lead, especially in the area of the places of adhesion between individual segments, to cracks through which moisture may penetrate.
As compared to this, this invention provides a covering, the material of which is exposed to considerably lower loads so that service life is increased and noise development may possibly be reduced.
To accomplish this, the casing or--in case of a multi-story tower--each section is attached only at its top or bottom rigidly to a supporting mechanism. Thus, an introduction of tensions into the casing, by relative movement between it and carrying mechanisms or other mutual supports, is avoided. Especially in the case of long antenna masts, a construction which permits free vertical movement, preferably of the upper edge of a section, makes lateral vibration deflections of the antenna mast possible without introducing tension or buckling stresses into the material of the casing. As a result, the covering even in stormy weather, produces no noise in a disturbing volume. Further, greatly increased service life of the covering results because of the considerable decrease of stress in the material. It is also possible to make a division of the casing or of the sections at a distance from the supports or the supporting mechanisms, and to place an expansion joint between the divisions of the casing. Depending on the situation of the individual case, a vertical and/or horizontal expansion joint may be selected in order to avoid a build-up of stress in case of relative movement of adjoining edges of the casing. It is essential that the expansion joint does not transfer any supporting force so that it is without tension and consequently may always accommodate the relative movement without thereby causing a condition essential to build-up of tension in the casing.
Further details, characteristics and advantages of the invention will be understood from the subsequent description of embodiments based on the drawings.